This invention relates to sockets for the mounting of electrical parts such as an IC package and obtaining an electrical connection with the electrical parts.
In the production of semiconductor parts, it is generally the case that the IC package prepared by resin sealing semiconductor integrated circuit chips (IC chips) are subjected to a reliability test called "burn-in" prior to their shipment. This "burn-in test is a functional test subjecting the chip to a temperature and voltage condition for the purpose of separating the good product from the bad product.
The construction of a conventional socket which has been used for such IC package mounting in the burn-in test is shown in FIGS. 8 through 11. FIG. 8 shows the plane view and FIG. 9 shows the side view of this conventional socket and FIGS. 10 and 11 are expanded partial cross-section views.
As shown in FIG. 9, this socket comprises a base 100 as the main socket body to be mounted on a substrate (which is not shown in the drawing) and a cover 102 which is mounted in a freely reciprocating manner with respect to this base 100. As shown in FIG. 8, a square opening 106 is provided on the cover 102 for taking out and inserting IC package 104 (reference should be made to FIGS. 10 and 11) in the main socket body. When the cover 102 moves vertically in relation to the base 100, the angular parts 106a at the four corners of this opening 106 are guided by the two sides 108a outside of four guides 108 that are erected on the base 100.
The upper surface of the base 100 as shown in these figures is constructed to mount an IC package 104 of the QFP (Quad-in-line Flat Package) type. Two sides 108b inside each of the guides 108 constitute an inclined surface, with a tapered groove 108c which expands downward forming an angular part. A corresponding angular part of IC package 104 is to be guided by these grooves 108c upon mounting and removing IC package 104 from the socket. In addition, an L-shaped rib 110 is provided close to the base of each groove 108 on the base 100. The IC package 104 is positioned on the upper surface of the base by these ribs 110. On the base 100, a plurality of contacts 112 corresponding to the row of lead terminals on each side of the IC package 104 are provided in a row.
The construction and action of each of the contacts 112 will be explained below by referring to FIGS. 10 and 11. The contacts 112 may be prepared by blanking them out of a thin sheet of an electrically conductive material such as beryllium copper or the like. The contacts comprise a base part 112a which is buried in the base 100, an arc spring part 112b that extends in a curved manner upward from the upper end of this base part 112a, a lever part 112c that extends upward in a generally straight line from the upper edge of this arc spring part 112b, a lead holding part 112d that extends horizontally from the upper edge of the arc spring part 112b toward the center of the socket and a hook-shaped contact 112e which is formed at the tip of this lead holding part 112d. Additionally, a socket terminal pin 112f of the contacts protrudes vertically downward from the lower end of the base end 112a.
Lever part 112c has a tip portion 112g which is constantly in contact with an inclined sliding surface 114a of a cam part 114 which is provided in a protuberant manner from the lower surface of the cover 102. At the time when the cover 102 makes a vertical movement as compared with the base 100, the tip 112g of the lever part 112c follows the inclined sliding surface 114a of the cam part 114, with a consequence that the lever part 112c moves changing its position. On the inclined sliding surface 114a, there is provided partition walls 114b which guide both of the sides of the lever 112c so as to prevent the neighboring contacts 112 from contacting each other. On base 100 there is provided a lead mounting surface 116. On lead mounting surface 116 of the base 100, there is also erected a set of partition walls 118 so that the contact part of each contact 112 will not touch the neighboring contact 112.
The operation and action of the socket at the time when an IC package is mounted will be explained below.
In a state when the IC package 104 is not mounted, the cover 102 is pushed down from the position shown in FIG. 10 to the position shown in FIG. 11. As a result of this downward movement of the cover the lever part 112c which slidingly contacts the inclined sliding surface 114a of the cover changes its position in a generally clockwise direction. Along with this lever part 112c, the arc spring 112b also changes it position, with a result that the arc is compressed and that the upper edge of the arc spring 112b or the lower edge of the lever part 112c moves downward.
Likewise, the contact part 112e at the tip of the lead holding part 112d changes its position moving in a clockwise direction.
In this state, contact part 112e of the contact 112 is rotated upward from the lead mounted surface 116 so that the IC package 104 can be inserted into the main socket through an opening 106 from above the cover 102. At this juncture, the IC package 104 is guided to the base 100 by the groove 108c on the inside angular part of the guide 108 and positioned on the base 100 by the rib 110. Upon insertion, the bent tip of each lead 104a of the IC package 104 is placed on the lead mounting surface 116 at a prescribed location on the side of the base 100.
FIG. 11 shows the state in which the IC package has been inserted into the main socket in this manner.
Next, the downward force of the cover 102 is released. Thereupon, the cover 102 rises to its original position due to recovering force of the arc spring part 112b of the contact 112. The contact 112 is restored approximately to the original shape with the tip contact part 112e of the lead holding part 112d compressively engaging the bent tip part of the lead 104a of the IC package 104, thereby establishing contact with the bent tip part.
FIG. 10 shows the state in which an electric connection has been established in this manner between the IC package 104 and the contact members of the main socket.
In order to remove the IC package 104 from the main socket, the cover 102 is once again pushed toward the base 100 and the tip contact part 112e of the contact 112 is lifted from engagement with the lead 104a of the IC package 104 with a result that the IC package 104 can be removed from the socket.
In the prior art socket, the contact 112 is moved from the original position in connection with the forward movement of the cover 102, thereby making it possible for the IC package 104 to be charged into or extracted from the base 102. Upon restoring the contact 112 to its original position in connection with the return movement of the cover 102, the contacting of the contact 112 with the lead 104a of the IC package 104 is obtained. In order to prevent each of the plurality contacts 112 from touching the neighboring contact 112, partition walls 118 and 114b are provided at an interval corresponding to the pitch of the leads 104a on the inclined sliding surface 114a of the cover 102 as well as the lead mounted surface 116 of the base 100.
With an increase in the degree of integration of the IC chips, the number of leads (pins) of the IC package have increased and thus the pitch between the leads has become narrower (smaller). This results in the partition walls 118 and 114b needing to be thinner and thinner. For example, for an IC package wherein the width of the lead 104a is 0.15 mm and the pitch between the leads is 0.3 mm, the gap between the contacts is approximately 0.15 mm with the partition walls 118 and 114b having to be formed in this gap. Since each contact 112 changes its position, a certain amount of clearance is also required. Thus, it becomes necessary to maintain the thickness of the partition walls 118 and 114b to less than approximately 0.11 mm. It is difficult to make these sockets with an ever decreasing thickness of the partition walls.